scenes photo from the set of Avengers: Infinity War. In it, he poses with Benedict Cumberbatch, Mark Ruffalo, and BD Wong.

However, more revealing than the characters of Doctor Strange, Iron Man, the Hulk, and Wong coming together on set is a detail spotted deeper in the photo. Sitting together in costume, Downey Jr. is sporting a shirt with a certain circular hole in the chest area.

Fans of the Marvel Cinematic Universe realzie Tony Stark had his arc reactor removed from his chest by the end of Iron Man 3. So, why does he have the reactor in his chest again in the photo below?

There are several go-to theories regarding the arc reactor resurfacing.

The first is that Tony has never fought an enemy such as Thanos, nor have any of the other Avengers. The villain will be the most formidable foe they have ever come across (with the exception of Strange's encounter with Dormammu). Tony might experience a change of heart, literally, regarding his suits in Spider-Man: Homecoming or early events of Avengers: Infinity War which lead to him needing a bit more power to take on the villain.

Then, there is the more farfetched possibility of Doctor Strange's Eye of Agamotto being taken from him by the Mad Titan. Such a move seems inevitable but the next part is where it gets a little less likely: Thanos sends the heroes to a point in time where Stark was relying on the arc reactor to keep himself alive.

Then, of course, there is the possible connection to needing the arc reactor and going to the cosmos. Tony only scratched the surface of taking his suit to space when he diverted a nuclear missile from New York City through a wormhole into space. His suit promptly shut down so, clearly, there is room for improvement.

For one reason or another, Tony Stark will be sporting an arc reactor in Avengers: Infinity War.

As the Avengers and their allies have continued to protect the world from threats too large for any one hero to handle, a new danger has emerged from the cosmic shadows: Thanos. A despot of intergalactic infamy, his goal is to collect all six Infinity Stones, artifacts of unimaginable power, and use them to inflict his twisted will on all of reality. Everything the Avengers have fought for has led up to this moment - the fate of Earth and existence itself has never been more uncertain.”

Avengers: Infinity War is described by Marvel Studios as the culmination of everything in the Marvel Cinematic Universe since Iron Man in 2008. The movie is filming now under directors Anthony and Joe Russo, from a screenplay by Christopher Markus and Stephen McFeely.

We have another two years of hard work to even finish these movies, and they [the actors] have a lot of hard work to do, so thats all we're thinking about, is completing those and delivering on the promise of those. Where it goes beyond that, we'll see

“So much happens in [the 3rd and 4th Avengers movies], as you can imagine, and so much is affected by it that we felt what better person to hold your hand and lead you into the next incarnation of the MCU, in a grounded, realistic manner, than Peter Parker?” Marvel Studios president Kevin Feige told io9. “So, coming out two months after Untitled Avengers, [that’s what] much of what the next Spider-Man film will be about.”

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“It was purposefully done like this,” Feige continued. “Like how the events of Captain America: Civil War impacted Peter as he was dropped off by Tony and expected to go back to continue his sophomore year, how the hell are the events of Infinity War and Untitled [Avengers] going to affect him as he, yes, goes back to his junior year?”